Could A Little Bit Of Fasting Bring A Lot Of Health Benefits?

Intermittent fasting has gotten a lot of attention in recent years, but much of the scientific research behind it has been in mice, not men. Now, a new study by a team at University of Southern California has looked at how the diet affects a number of health markers in humans over the short term. And verdict is pretty encouraging, at least on its face: Not only is it good for one’s weight, but it seems to benefit other markers of health, including the risk of heart disease, cancer and diabetes. Whether it’s fundamentally better than the old way—keeping at a healthy weight, eating well and exercising—is another question.

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The team had 100 people continue with their regular diets for three months, or do three cycles of the Fasting Mimicking Diet (FMD), which includes normal eating for most of the month and then five days of a semi-fasting regimen. During these five days, the participants weren’t actually starving themselves, but ate a ProLon diet, which was developed by the researcher who led the study, Valter Longo (but who’s quick to point out he does not make money from the product). The very-low-calorie items included energy bars, energy drinks, vegetable-based soups and supplements—everything is low in sugars and proteins, but high in healthy unsaturated fats.

At the end of the three months, people doing the FMD had some significant changes: On average they’d lost 5.7 pounds; had lower levels of insulin-like growth factor 1 (IGF-1), a hormone linked to cancer and aging; and C-Reactive Protein (CRP), a marker of inflammation. They also had lower body mass index (BMI), trunk fat, waist circumference, blood pressure and cholesterol. People in the control group didn’t have the same changes, of course, but when they were later switched to the FMD, their numbers also improved similarly.

The team’s previous work has found that a fast-mimicking diet is linked to health benefits in almost every system of the body and to longer lifespan, at least in rodents. And the new study seems to suggest that humans may reap similar benefits, although very-long-term trials have not yet been done in people.

Longo says enough research is behind the diet that he’d recommend people try a partial fast like the one used in the trial, but it need not be done every month. He says anywhere from two to 12 times a year could be effective, depending on one’s variables—age, weight and existing health concerns. “But,” Longo adds, “the decision should be left to the doctor or registered dietitian. For example, someone who is obese and who has high cholesterol and fasting glucose may want to consider doing it once a month whereas an athlete who eats a very healthy diet and is in perfect shape may only do it twice a year.”

He adds that a true fast, of just water or an otherwise extreme version of a fast, can be dangerous. And he recommends talking to a doctor before doing anything.

But not everyone is so convinced that even a partial fast is necessary. A potential shortcoming of the current study is that the people in the control group initially ate as they always did—they didn’t reduce their calories. So technically, it’s not clear whether the benefit of the FMD came from the fasting or the general reduction in calories which we already know helps almost every measure of health.

“As far as I can tell, this proves nothing about fasting,” says David L. Katz, founding director of the Prevention Research Center at Yale University and a Forbes contributor. “Going days without food produces a calorie deficit, and that causes weight loss. Weight loss, in turn, ameliorates all of the metabolic markers studied here. So, what we've got is: eating less leads to short-term weight loss, and weight loss improves diverse metabolic markers in the short term. Which part of that didn't we know already? To show direct benefit of fasting, it needs to outperform an alternative diet pattern matched for calories. That was not done here.”

Still, earlier studies have suggested that calorie restriction is linked to reduced risk of disease and to a longer lifespan. A study last month showed that long-term calorie restriction in a monkey led a considerably (and record-breaking) longer life. More work will need to be done to look at how the current study’s partial five-day fast might work out over the very long term—over decades, when health outcomes can actually be measured and not just predicted. In the meantime, eating a plant-based diet and getting to a healthy weight (and, of course, exercising) may be the best way. It’s definitely stood the test of time.